The skin is a complex and dynamic organ that provides a highly regulated interface between the external and internal environment. Skin aging is a multi-factorial process and proceeds as a function of both intrinsic stressors such as free-radical generation from metabolic and catabolic processes, and extrinsic stressors such as chemical and UV-light exposure and generation of free radicals at the surface, as well as from genetic determinism. Wrinkles, loss of tone and firmness, a decrease in moisture retention capacity, and development of pigment irregularities, are all well-known age-related effects that underpin an appearance of “aged skin.”
Given the significant impact that skin aging can have on one's appearance and self esteem, there is an ongoing effort to identify cosmetic agents and develop formulations that are effective at treating or improving the appearance of aging skin. Scientists have established that skin aging results from multiple biological mechanisms, and that countering or reversing the effects of aging must be addressed by a multi-mechanistic approach. Hence, over the past several decades the focus has been on formulating skin anti-aging compositions based on identifying the underlying processes implicated in the appearance of aging skin, and developing or identifying skin care agents that specifically counter or shift the equilibrium in these processes toward a more youthful appearance.
An early approach to cosmetic product development reflecting the multi-mechanistic paradigm was to formulate a single composition with several skin-care actives identified as effective for different or multiple mechanisms. Application regimens generally involved multiple applications of the same formulation across a dosing or treatment time frame. Another early product development approach was simply to add identified actives to existing delivery products in order to piggyback off existing consumer habits, such as routine application of morning moisturizers and night eye-creams. Many cosmetic products are now available to consumers that have been formulated with multiple anti-aging skin care agents; however interaction of biological processes activated by agents in the same formulation or between formulations in accordance with any particular application regimen was not scientifically investigated.
Recently, scientists at Tulane University demonstrated anti-aging efficacy in a regimen involving daily application of multiple compositions, each composition formulated to deliver certain actives at times theoretically linked with an optimal benefit effect. The study investigated the impact of application of four different product formulations, a cleanser, day-cream, night-cream, and eye-cream on a daily basis. Each product was known and contained actives with established mechanistic-based benefits, and each product was already marketed as having a daily preferred time for application. In the experimental protocol, control subjects were provided formulations comprising the same delivery vehicles and excipients, including sun screen, without the actives (J Drugs Dermatol. 2012; 11(12):1447-1454) and all subjects were instructed to follow a regimen comprising application of each formulation at a specific time of day for up to 30 weeks. This study, however, failed to consider or control for any effect specifically due to the regimen. Both experimental and control subjects followed the same application regimen, and there was no control population enabling comparison of order of application of specific actives and/or for investigation of any differential effect on target benefit that may have been conferred (or compromised) by order of application. Further, although the study noted the theoretical bio-mechanistic basis for inclusion of the eight active ingredients in the four compositions, there was no scientific foundation based on interplay between or among the mechanisms suggested or confirmed as a basis for an application regimen and in particular from the order of application of the actives.
Skin care regimens suggesting use of an exfoliating agent along with surfactants/soaps in a skin cleansing formulation prior to application of anti-aging formulations are also known in the art. However, known cleansing formulations suffer from the lack of scientific insight/foresight or basis with respect to what actives or mechanistic manipulations/effects in addition to cleansing might provide additional priming of the skin for receptivity to subsequently delivered actives present in a second formulation. Most particularly, formulation of compositions as part of specific multi-step regimens based on interaction between actives and the biological processes/mechanisms they regulate/activate have not been considered. In part this was due to difficulty in perceiving the more subtle interactions and variances among cosmetic agents and the processes they regulate.
More recently, however, cosmetic investigators have been able to validate biological process regulation by cosmetic actives through gene transcriptional studies. The principles of genetics and transcriptional regulation have been applied to designing and validating skin anti-aging formulations. Generally, these studies were based on global micro-array analyses of treated skin versus untreated skin and identification of genes differentially regulated in response to the treatment. In even more refined studies including studies by some of the present investigators, methods and formulations based on identification and categorization of skin care agents according to ability to transcriptionally regulate genes implicated in specific biological pathways known to be associated with skin health and functioning were developed and/or validated (see, e.g., application Ser. No. 13/022,191). However, although active synergies were sometimes be observed, mechanistic interaction between actives and interplay between the implicated biological processes when actives are co-formulated or applied in tandem or according to specific application regimens were not considered.
Surprisingly, by application of recently developed principles of bioinformatics that refine the genetic model, it has now been found that order of application of specific skin-care actives can be manipulated to achieve an enhanced anti-aging benefit over random or reverse application of the same actives across a daily dosing treatment time frame protocol.
Under the current model, genes and gene expression products may be grouped according to biological pathways, processes or “themes” in which expression regulation by an active is implicated. According to a relatively new bioinformatics-generated genetic model, “eigengenes” may be derived to elucidate relationships between the pathways (Langerfelder and Hovarth, BMC Systems Biology 2007, 1:54, 1752-0509). Under the Eigengene model, a “module” is a group of interconnected genes that forms a biological pathway, process or theme, and an intersecting set of two or more modules is called a “co-expression module.” A gene expression profile of a module or co-expression module may be represented by an “eigengene,” and eigengene networks may be constructed to represent the relationships between and within genetic co-expression modules. Derivation of an “eigengene” collapses many data points into a single vector. An eigengene may be thought of as a summary of a module expression profile into a single representative gene. An eigengene reflects the variance between the genes comprising the modules.
The present investigators posited that even the subtle impact of interactions between biological processes triggered by cosmetic actives may be studied by applying these principles to investigation of cosmetic anti-aging formulations and regimens. Surprisingly, it was discovered that order of topical application of skin care compositions comprising anti-aging actives makes a difference in the efficacy of the overall treatment benefit, and that formulations may be developed to maximize the effect of regimen on the anti-aging benefit.